Improvement of Eurocode 8 Seismic Design Envelope for Bending Moments in RC Walls of High-rise Buildings

ABSTRACT

The paper focuses on the analysis of actual bending moments in RC walls of high-rise structures. A comprehensive analysis was carried out on three concrete buildings in order to evaluate the accuracy of the procedure for obtaining bending moments proposed by Eurocode 8 (EC8). The buildings are designed according to EC8 for medium ductility class (DCM) and high ductility (DCH). Nonlinear 3D models of the selected structures were subjected to 60 strong earthquake ground motions recorded on rock and stiff soil. One hundred and eighty nonlinear time-history analyses (NTHA) are carried out to compare the actual bending moments against design EC8 bending moments. Based on the findings of the conducted study, the possible improvement of EC8 bending moments design envelope for RC walls of high-rise buildings is indicated. A simple proposal for the correction of the existing EC8 bending moment envelope is introduced by its modification over the height of the wall to account bending moment increase due to the higher mode effects and by substituting EC8 design moment with wall resistance moment at the base. This improved envelope better matches the actual bending moments in RC walls of high-rise buildings. Further calibration is clearly required.

KEYWORDS:

• High-rise buildings
• RC walls
• bending moments
• seismic design
• Eurocode 8 (EC8)
• non-linear time-history analysis (NTHA)

Abbreviations

CoV Coefficient of variation

DCM Medium ductility class

DCH High ductility class

EC8 Eurocode 8

MSE Mean squared error

NTHA Nonlinear time-history analysis

RC Reinforced concrete

RSA Response spectrum analysis

SW₁ Shear wall 1

SW₂ Shear wall 2

List of symbols

$a_I^{\hspace{0.17em}}$    Tension shift for design envelope according to EC8

$A_{fr}^{\hspace{0.17em}}$     Flexural reinforcement in the confined boundary elements

$A_{wr}^{\hspace{0.17em}}$     Vertical web reinforcement of the walls

$E_{cm}^{\hspace{0.17em}}$     Modulus of elasticity of concrete

$f_{\hspace{0.17em}}^{\hspace{0.17em}}$    Linear scaling factor

$f_{ck}^{\hspace{0.17em}}$     Characteristic compressive cylinder strength of concrete

$f_{cm}^{\hspace{0.17em}}$     Mean value of concrete cylinder compressive strength

$f_{yk}^{\hspace{0.17em}}$     Characteristic yield strength of reinforcement

$f_{ym}^{\hspace{0.17em}}$     Mean value of yield strength of reinforcement

$M_{\hspace{0.17em}}^{\hspace{0.17em}}$     Magnitude

$M_{Ed}^{\prime }$   Moment diagram from linear analysis according to EC8

$M_{Ed}^{{ }^{\prime \prime }}$   Design EC8 envelope without tension shift

$M_{Ed}^{\hspace{0.17em}}$   Design EC8 envelope

$M_{na}^{\hspace{0.17em}}$   Mean value of bending moments obtained from NTHA

$M_{Ed,priestley}^{\hspace{0.17em}}$  Bending moments obtained by Priestley procedure

$M_{Rd}^{\hspace{0.17em}}$   Design moment resistance

$M_{fy}^{\hspace{0.17em}}$    First yield bending moment of the wall section

$M_{Ed,hrb}^{\hspace{0.17em}}$    The proposed design bending moment envelope

R   Distance from fault

T₁   Fundamental period of the building

q   Behaviour factor